Princeton University professor Jason Petta and his team have developed a method that could eventually enable engineers to build a working quantum computer comprising millions of qubits. “The whole game at this point in quantum computing is trying to build a larger system,” says Andrew Houck, who is part of the research team at the university. To this end, Petta’s team used a stream of microwave photons to analyze a pair of electrons trapped in a tiny cage called a quantum dot. The “spin state” of the electrons serves as the qubit, and the microwave stream enables the scientists to read that information. “We create a cavity with mirrors on both ends–but they don’t reflect visible light, they reflect microwave radiation,” Petta says. “Then we send microwaves in one end, and we look at the microwaves as they come out the other end. The microwaves are affected by the spin states of the electrons in the cavity, and we can read that change.” He says the next step is to increase the reliability of the setup for a single electron pair and to add more quantum dots to create more qubits.